What is a radio frequency circuit.alarm sensor sales

　　Radio frequency is abbreviated as RF, radio frequency is radio frequency current, it is an abbreviation of high-frequency alternating electromagnetic wave. The alternating current that changes less than 1000 times per second is called low-frequency current, and the alternating current that changes more than 1000 times is called high-frequency current, and radio frequency is such a high-frequency current.

　　RF circuit refers to a circuit whose electromagnetic wavelength and the size of the circuit or device are in the same order of magnitude. At this time, due to the relationship between the size of the device and the size of the wire, the circuit needs to be dealt with by the related theory of distributed parameters. This type of circuit can be considered as a radio frequency circuit without strict requirements on its frequency, such as long-distance AC transmission lines (50 or 50 or 50). 60Hz) Sometimes it is also dealt with by the related theory of RF.

　　1. The structure and working principle of the receiving circuit:

　　When receiving, the antenna converts the electromagnetic wave sent from the base station into a weak AC current signal, filtered, amplified by high frequency, and sent to the intermediate frequency for demodulation to obtain the receiving baseband information (RXI-P, RXI-N, RXQ-P, RXQ- N); sent to the logic audio circuit for further processing.

　　circuit analysis:

　　(1) Circuit structure

　　The receiving circuit is composed of antenna, antenna switch, filter, high-frequency amplifier tube (low noise amplifier), intermediate frequency integrated block (receiving demodulator) and other circuits. Early mobile phones had primary and secondary mixing circuits, whose purpose was to lower the receiving frequency and then demodulate (as shown in the figure below).

　　2. The structure and working principle of the transmitting circuit

　　During transmission, the transmission baseband information processed by the logic circuit is modulated into the transmission intermediate frequency, and the transmission intermediate frequency signal is changed to a frequency signal of 890M-915M (GSM) with TX-VCO. After being amplified by the power amplifier, the antenna is converted into electromagnetic waves and radiated out.

　　circuit analysis:

　　(1) Circuit structure.

　　The transmitting circuit is composed of the internal transmitting modulator and transmitting phase detector; transmitting voltage controlled oscillator (TX-VCO), power amplifier (power amplifier), power controller (power control), transmitting transformer and other circuits

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